Thermal performance of cast-in-place piles with artificial ground freezing in permafrost regions

During the construction of cast-in-place piles in warm permafrost,the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost.Since the bearing capacity of the pile is quite small before the full freeze-back,the quick refreezing of the native soils surrounding the cast-in-place pile has become the focus of the infrastructure construction in permafrost.To solve this problem,this paper innovatively puts forward the application of the artificial ground freezing(AGF)method at the end of the curing period of cast-in-place piles in permafrost.A field test on the AGF was conducted at the Beiluhe Observation and Research Station of Frozen Soil Engineering and Environment(34°51.2'N,92°56.4'E)in the Qinghai Tibet Plateau(QTP),and then a 3-D numerical model was established to investigate the thermal performance of piles using AGF under different engineering conditions.Additionally,the long-term thermal performance of piles after the completion of AGF under different conditions was estimated.Field experiment results demonstrate that AGF is an effective method to reduce the refreezing time of the soil surrounding the piles constructed in permafrost terrain,with the ability to reduce the pile-soil interface temperatures to below the natural ground temperature within 3 days.Numerical results further prove that AGF still has a good cooling effect even under unfavorable engineering conditions such as high pouring temperature,large pile diameter,and large pile length.Consequently,the application of this method is meaningful to save the subsequent latency time and solve the problem of thermal disturbance in pile construction in permafrost.The research results are highly relevant for the spread of AGF technology and the rapid building of pile foundations in permafrost.

Seismic performance analysis and design suggestion for frame buildings with cast-in-place staircases

Many staircases in reinforced concrete （RC） frame structures suffered severe damage during the Wenchuan earthquake. Elastic analyses for 18 RC structure models with and without staircases are conducted and compared to study the influence of the staircase on the stiffness, displacements and internal forces of the structures. To capture the yielding development and damage mechanism of frame structures, elasto-plastic analysis is carried out for one of the 18 models. Based on the features observed in the analyses, a new type of staircase design i.e., isolating them from the master structure to eliminate the effect of K-type struts, is proposed and discussed. It is concluded that the proposed method of staircase isolation is effective and feasible for engineering design, and does not significantly increase the construction cost.

Field observation of the thermal disturbance and freezeback processes of cast-in-place pile foundations in warm permafrost regions

The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations.The construction process and the hydration heat of cast-in-place(CIP)pile foundations affect the thermal stability of permafrost.In this paper,temperature data from inside multiple CIP piles,borehole observations of ground thermal status adjacent to the foundations and local weather stations were monitored in warm permafrost regions to study the thermal influence process of CIP pile foundations.The following conclusions are drawn from the field observation data.(1)The early temperature change process of different CIP piles is different,and the differences gradually diminish over time.(2)The initial concrete temperature is linearly related with the air temperature,net radiation and wind speed within 1 h before the completion of concrete pouring;the contributions of the air temperature,net radiation,and wind speed to the initial concrete temperature are 51.9%,20.3%and 27.9%,respectively.(3)The outer boundary of the thermal disturbance annulus is approximately 2 m away from the pile center.It took more than 224 days for the soil around the CIP piles to return to the natural permafrost temperature at the study site.

基于Stair−YOLOv7−tiny的煤矿井下输送带异物检测

针对现有煤矿井下输送带异物检测方法应对复杂场景适应性差、无法满足实时性和轻量化要求、处理尺寸差异较大异物时表现不佳的问题,基于轻量化YOLOv7−tiny模型进行改进,提出了一种Stair−YOLOv7−tiny模型,并将其用于煤矿井下输送带异物检测。该模型在高效层聚合网络(ELAN)模块中添加特征拼接单元,形成阶梯ELAN(Stair−ELAN)模块,将不同层级的低维特征与高维特征进行融合,加强了特征层级间的直接联系,提升了信息捕获能力,增强了模型对不同尺度目标和复杂场景的适应性;针对检测头引入阶梯特征融合(Stair−fusion),形成阶梯检测头(Stair−head)模块,通过逐层融合不同分辨率的检测头特征,增强了中低分辨率检测头的特征表达能力,实现了特征信息的互补。实验结果表明:Stair−YOLOv7−tiny模型在输送带异物开源数据集CUMT−BelT上的检测效果优于CBAM−YOLOv5,YOLOv7−tiny及其轻量化模型,准确率、平均精度均值、召回率和精确率分别达98.5%,81.0%,82.2%和88.4%,检测速度为192.3帧/s;在某矿井下输送带监控视频分析中,Stair−YOLOv7−tiny模型未出现漏检或误检,实现了输送带异物的准确检测。

Refreezing of cast-in-place piles under various engineering conditions

In the construction of the Qinghai-Tibet Power Transmission Line （QTPTL）, cast-in-place piles （CIPPs） are widely applied in areas with unfavorable geological conditions. The thermal regime around piles in permafrost regions greatly affects the stability of the towers as well as the operation of the QTPTL. The casting of piles will markedly affect the thermal regime of the surrounding permafrost because of the casting temperature and the hydration heat of cement. Based on the typical geological and engineering conditions along the QTPTL, thermal disturbance ofa CIPP to surrounding permafrost under different casting seasons, pile depths, and casting temperatures were simulated. The results show that the casting season （summer versus winter） can influence the refreezing process of CIPPs, within the first 6 m of pile depth. Sixty days after being cast, CIPPs greater than 6 m in depth can be frozen regardless of which season they were cast, and the foundation could be reffozen after a cold season. Comparing the refreezing characteristics of CIPPs cast in different seasons also showed that, without considering the ground surface conditions, warm seasons are more suitable for casting piles. With the increase of pile depth, the thermal effect of a CIPP on the surrounding soil mainly expands vertically, while the lateral heat disturbance changes little. Deeper, longer CIPPs have better stability. The casting temperature clearly affects the thermal disturbance, and the radius of the melting circle increases with rising casting temperature. The optimal casting temperature is between 2 ℃ and 9 ℃.

Physical modeling of behaviors of cast-in-place concrete piled raft compared to free-standing pile group in sand

Similar to free-standing pile groups, piled raft foundations are conventionally designed in which the piles carry the total load of structure and the raft bearing capacity is not taken into account. Numerous studies indicated that this method is too conservative. Only when the pile cap is elevated from the ground level,the raft bearing contribution can be neglected. In a piled raft foundation, pileesoileraft interaction is complicated. Although several numerical studies have been carried out to analyze the behaviors of piled raft foundations, very few experimental studies are reported in the literature. The available laboratory studies mainly focused on steel piles. The present study aims to compare the behaviors of piled raft foundations with free-standing pile groups in sand, using laboratory physical models. Cast-in-place concrete piles and concrete raft are used for the tests. The tests are conducted on single pile, single pile in pile group, unpiled raft, free-standing pile group and piled raft foundation. We examine the effects of the number of piles, the pile installation method and the interaction between different components of foundation. The results indicate that the ultimate bearing capacity of the piled raft foundation is considerably higher than that of the free-standing pile group with the same number of piles. With installation of the single pile in the group, the pile bearing capacity and stiffness increase. Installation of the piles beneath the raft decreases the bearing capacity of the raft. When the raft bearing capacity is not included in the design process, the allowable bearing capacity of the piled raft is underestimated by more than 200%. This deviation intensifies with increasing spacing of the piles.

A Comparison of Pound's Poetic Ideas and Some Chinese Poetic Principles-Using the Translation of "The Jewel Stairs' Grievance" as a Case in Point

The prominent features of Li Bai's "The Jewel Stairs'Grievance" are precise diction;implicit meaning;an absent narrator;and a seamless unity of images and feelings.Pound's translation of it in Cathay reveals some kind of connections between some Chinese poetic principals and Pound's individual poetics.

Practical Use of Stairs to Assess Fitness, Prescribe and Perform Physical Activity Training

Aim: Evaluating climbing stairs for prescription and implementation of physical activity regimes. Methods: Healthy females (F, n = 14), and males (M, n = 15) participated. By climbing 100 steps of stairs with 0.173 m height, Heart rate (HR) and oxygen uptake were measured throughout the floors;Blood pressure (BP) was measured at ground and the 5th floors only. Results: Energy increased from 2 to 7.6 was metabolic equivalents (METs = 3.5 ml O2/min.kg) at 17.3 m elevation in 2 min. at the 5th floor, and percent Heart Rate Reserve (%HRR) was 66.17% in F and 48.7% in M, proportional to their aerobic efforts. Average climbing efficiency was 15.8 ± 2.3% (n = 29). Aerobic capacity estimated dividing the highest work rate (17.3 Kg.m/2min.Kg × 0.00239 = 0.0207 Kcal/min.Kg), by fractional effort (F = 0.6617, M = 0.487) and fractional efficiency (0.158), at 5 Kcal/L O2 was 0.040 in F and 0.054 L O2/Kg.min in M. Minimum training intensity reached at the 3rd floor by F. In M the highest %HRR reached was 48.7% at the 5th floor, insufficient for training. Conclusions: Stairs used for submaximal evaluation of aerobic capacity and for target intensity prescription. Training, levels climbed, repetitions per day (if 5, 100 Kcal per day, ascending) and number of days/week are adjusted. Full regime requires up to 7.6 METs, a total of 532 and 140 MET.min/week ascending and descending, respectively. Intensities >7.6 MET, climbing rate should be >8.65 m/min. Limiting ascent to 1 (3.5 METs) or 2 (5.5 METs) floors or only descents (2 - 3 METs) may be used for unfit subjects. This method is useful for those with no access to sophisticated facilities.

Field study of plastic tube cast-in-place concrete pile

The compositions, technical principles and construction equipments of a new piling method used for ground improvement plastic tube cast-in-place concrete pile were introduced. The results from static load tests on single piles with different forms of pile shoes and on their composite foundations were analyzed. The distribution patterns of axial force, shaft friction and toe resistance were studied based on the measurements taken from buried strain gauges. From the point of engineering application, the pile has merits in convenient quality control, high bearing capacity and reliable quality, showing higher reasonability, advancement and suitability than other ground improvement methods. The pile can be adopted properly to take place of ordinary ground improvement method, achieving greater economical and social benefits.

Form Art and Function Analysis of Outdoor Stairs

Stairs are an important structural component in the architectural space design.It not only serves as a link between landscapes,but also a highlight of the space.Interpretation of stairs can be carried out from the form and function of stairs.This paper mainly takes the outdoor stairs as the research object,which is a building component to solve the vertical traffic function of the building,and selects some stairs designs worldwide for the analysis.Focusing on architectural design,the study investigates the expression form of each component of the outdoor stairs,and explores the diversified designs of the stairs.The paper urges designers to pay close attention to the problems of stair design in essence,to deeply understand the forms and methods of stair expression,to expand the breadth of architectural design thinking,to pursue in-depth understanding of the inherent laws of building generation,and to improve the quality of architecture.

Design and construction of high and large span cast-in-place reinforced concrete cantilever flowering frame beam

The high and large span cast-in-place reinforced concrete cantilever structure of the office building of some court, which is located I-steel at the cantilever and used steel pipe scaffold as the support, has guaranteed the frame body and structure security by the frame body calculating, on-site test and reasonable construction order.

Stair climbing,genetic predisposition,and the risk of incident type 2 diabetes:A large population-based prospective cohort study

Background:Cross-sectional evidence and small-scale trials suggest positive effects of stair climbing on cardiometabolic disease and glucose regulation.However,few studies have examined the long-term association between stair climbing and the incidence of type 2 diabetes(T2D).We aimed to prospectively evaluate the association of stair climbing with T2D and assess modifications by genetic predisposition to T2D.Methods:We included 451,699 adults(mean age=56.3±8.1 years,mean±SD;55.2%females)without T2D at baseline in the UK Biobank and followed up to March 31,2021.Stair climbing information was collected through the touchscreen questionnaire.Genetic risk score for T2D consisted of 424 single nucleotide polymorphisms.Results:During a median follow up of 12.1 years,14,896 T2D cases were documented.Compared with participants who reported no stair climbing,those who climbed stairs regularly had a lower risk of incident T2D(10-50 steps/day:hazard ratio(HR)=0.95,95%confidence interval(95%CI):0.89-1.00;60-100 steps/day:HR=0.92,95%CI:0.87-0.98;110-150 steps/day:HR=0.86,95%CI:0.80-0.91;>150 steps/day:HR=0.93,95%CI:0.87-0.99,p for trend=0.0007).We observed a significant interaction between stair climbing and genetic risk score on the subsequent T2D risk(p for interaction=0.0004),where the risk of T2D showed a downward trend in subjects with low genetic risk and those who reported stair climbing activity of 110-150 steps/day appeared to have the lowest overall T2D risk among those with intermediate to high genetic risk.Conclusion:A higher number of stairs climbed at home was associated with lower T2D incidence risk,especially among individuals with a low genetic predisposition to T2D.These findings highlight that stair climbing,as incidental physical activity,offers a simple and low-cost complement to public health interventions for T2D prevention.

地下隧道竖向疏散现场试验研究

近年来,隧道的疏散设计中普遍应用竖向疏散模式,但该模式的安全性缺少真实试验数据支撑和验证。为探究隧道竖向疏散模式下的人员疏散行为特征及关键参数,采用现场试验的方法,在某隧道内搭建火灾时的交通堵塞场景,组织188名参与者(109名男性,79名女性)开展大规模人群疏散研究,针对人员疏散时间、疏散行走速度、疏散楼梯人员通行能力、疏散楼梯盖板开启时间等参数进行分析。研究结果表明:1)隧道火灾时,人员疏散受到隧道熟悉度和疏散引导的显著影响,在紧急疏散过程中更容易发生拥堵,疏散引导可极大地改善人员的出口及路径选择,提高疏散效率。2)交通堵塞状态下,人员疏散行走速度因隧道熟悉度的提高和疏散引导而显著提高。行车道上,男性和女性的平均速度分别由1.38 m/s、1.39 m/s提高至1.94 m/s、1.99 m/s。但在下部安全疏散通道内,参与者出现懈怠和放松的情绪,平均疏散行走速度会略有降低。应考虑在疏散通道内设置一些警示标志以督促引导人员疏散。3)入口宽度为1.09 m的疏散楼梯的最大人员通行能力为38人/min;男性参与者开启楼梯盖板的平均时间为7.5 s,女性参与者开启楼梯盖板的平均时间为12.6 s,相比于女性,男性参与者更容易打开楼梯盖板。研究结果可为隧道疏散逃生方案设计、运营管理提供真实试验数据参考,提高隧道防灾疏散水平。

阿基米德螺线变形轮的设计与研究

针对轮组式、轮履复合式和轮腿复合式等传统爬楼机构对楼梯适应能力不足以及体积笨重的问题,以攀爬楼梯为首要任务和设计目的,提出了一种新型楼梯越障机构——阿基米德螺线变形轮。该变形轮不仅能够较好地适应楼梯这种复杂环境,而且结合了轮式行进机构的强机动性与螺线行进机构的优良越障性。使用SoildWorks软件对变形轮机构和总体装配方案进行设计;根据运动环境和越障过程对变形轮进行参数计算和数据分析,优化了变形轮翻越连续台阶过程;最后,应用Adams软件对变形轮越障过程进行仿真分析,并将行星轮和变形轮进行对比仿真,证明了设计与研究的有效性。仿真结果证明,所设计的变形轮具有较强的机动性与稳定性。

阶梯碳下考虑耦合电转气-碳捕集和热电联产灵活输出的综合能源系统优化调度

“双碳”目标下,为进一步降低综合能源系统(integrated energy system,IES)碳排放,提升可再生能源消纳能力,提出一种IES低碳经济运行优化策略。首先引入阶梯型碳交易机制约束IES的碳排放;然后建立耦合电转气(power to gas,P2G)和碳捕集系统(carbon capture system,CCS)模型,并细化P2G两阶段运行;接着在传统热电联产机组(combined heat and power,CHP)中引入卡琳娜循环与电锅炉联合运行,构造热电灵活输出的CHP模型;最后以系统运维成本、碳交易成本、购能成本和弃风弃光成本之和最小为优化目标,构建IES低碳经济调度模型,并设置不同运行场景对比分析。结果表明:IES碳排放减少38.45%,运行总成本降低10.37%,验证了所建模型的低碳性和经济性。

偏瘫患者下台阶过程下肢生物力学特征分析

目的对比分析偏瘫患者以不同方式下台阶过程中下肢生物力学特征,为降低患者下台阶过程中的跌倒风险提供理论依据。方法选取10名正常人和20名符合要求的偏瘫患者,使用Qualisys动作捕捉系统和Kistler三维测力台对受试者下台阶过程中的运动学和动力学数据进行收集,分析其在下台阶过程中的生物力学特征和跌倒风险。结果相较于正常人和先用健足下台阶(steps on the healthy side,SHS),先用患足下台阶(steps on the affected side,SAS)时,患侧下肢各关节屈伸活动幅度较小;SHS降低了健侧膝关节屈伸活动幅度,患侧下肢各关节屈伸活动幅度较SAS大;SAS下台阶左右方向地面反作用力(ground reaction force,GRF)曲线变化与正常人较为一致,患侧落地瞬间垂直GRF最大为1.05倍体重,健侧为1.25倍体重,低于正常人(1.5倍体重);SHS下台阶健侧落地瞬间最大垂直GRF为1.85倍体重,高于SAS和正常人。结论相较于SAS,患者使用SHS下台阶患侧关节活动幅度和落地瞬间垂直GRF较大,更难掌握。SAS更符合偏瘫患者下台阶的生物力学特征。

单间室与全膝关节置换术对膝骨关节炎患者楼梯行走时生物力学特征的影响

目的探究单间室膝关节置换术(unicompartmental knee arthroplasty,UKA)与全膝关节置换术(total knee arthroplasty,TKA)对膝骨关节炎术后的临床疗效。方法随机招募TKA患者21例、UKA患者15例。分别在术前以及术后6、12个月进行生物力学测试。采用Vicon红外动作捕捉系统和Kistler三维测力台同步采集受试者楼梯行走的运动学和动力学数据。结果在上楼梯时,TKA组受试者术前膝屈曲力矩峰值显著低于UKA组,术后6个月到达膝屈曲/内收力矩峰值时间、膝屈曲力矩冲量及膝内收力矩峰值负载率显著小于UKA组。在下楼梯时,UKA组术前和术后6个月伸膝功率峰值显著较小,垂直地面反作用力峰值负载率术前显著较大,膝伸展力矩峰值术后6个月显著较大;在术后12个月,楼梯行走的生物力学特征未出现明显的差异性。结论TKA组和UKA组在手术后表现出相似的膝关节功能,但TKA组可能采取不同于UKA组的下肢生物力学模式。在楼梯行走时,UKA组术后表现出更好的股四头肌控制能力,提高了楼梯行走尤其是下楼梯的姿势控制能力,而TKA组则采取保守的楼梯步态策略以降低楼梯行走的膝关节负荷。相比于力矩峰值,到达力矩峰值的时间及力矩峰值负载率是发现膝关节负荷差异性更灵敏的指标。

楼梯处行人行为对高层建筑应急疏散的影响研究

为研究人员密集情况下楼梯处行人行为对应急疏散的影响,通过现场观测获得某9层建筑楼梯处行人的个体和群体移动特征和基本运动参数,采用社会力模型和Anylogic 8.3软件构建楼梯疏散模型,模拟研究建筑疏散用时和楼梯处拥堵情况。研究表明:楼梯处行人行进速度与人流密度呈反比,上楼速度受人流密度影响较大,下楼时男女速度存在显著性差异,且男性行进速度离散型大于女性;楼梯中间平台是疏散过程中主要的拥堵地点;9层建筑的第四层为最大拥堵点,人员到达第四层向下疏散的用时明显加长,疏散压力较大。建议高层建筑疏散过程中在中间楼层设置疏散引导人员,做好对人群的引导和安抚工作。

基于局部模型网络的主汽温阶梯式动态矩阵控制

火电厂主汽温系统的大惯性、时变性和多扰动等特点导致采用传统串级PID控制难以取得令人满意的控制效果。为了克服传统控制方案的缺陷,提出了一种基于局部模型网络的多模型阶梯式动态矩阵控制算法。首先,通过引入阶梯式策略有效解决了原始动态矩阵控制算法固有的矩阵求逆问题;其次,通过引入扰动前馈补偿,提高了主汽温系统的抗扰动能力;最后,针对不同工况下动态特性大幅度变化的主汽温对象,设计了基于局部模型网络的多模型阶梯式动态矩阵控制器。仿真结果表明,相比于传统控制算法,所提算法明显提升了主汽温系统的全局设定值跟踪性能、抗扰动性能和鲁棒性能,可以满足火电机组主汽温的控制要求。

老年人上下楼梯肌肉激活特征与跌倒风险的关系

背景:在楼梯步行中,不同肌肉协同工作、相互代偿,衰弱的肌肉力量是否真正影响老年人楼梯跌倒风险尚不清楚。利用实时老年人楼梯步行的肌电信号来反映老年人楼梯步行中跌倒风险高低,或许可以进一步提升预测方法的准确性。目的:探究楼梯行走过程中老龄化对老年人下肢肌肉激活的影响,并分析其肌肉激活特征与楼梯跌倒风险的关系。方法:受试者按年龄分为老年组(n=19)和青年组(n=18),要求以自然速度上下10个台阶的楼梯,结合表面肌电技术采集楼梯步行肌电信号计算均方根(RMS),分析肌肉激活程度的差异。利用logistic回归分析,纳入股外侧肌和腓肠肌RMS建立老年人楼梯跌倒风险预测模型,通过受试者工作特征曲线及曲线下面积评价模型的区分度,采用Hosmer-Lemeshow检验评价模型的拟合度。结果与结论:(1)老年人上、下楼梯时股直肌(Z=-3.464,P=0.001;t=3.379,P=0.002)和腓肠肌外侧(Z=-2.978,P=0.003;Z=-3.555,P <0.001)激活程度高于年轻人;(2)老年人上楼梯胫骨前肌(Z=-2.350,P=0.019)和腓肠肌内侧(Z=2.321,P=0.020)、外侧(t=3.158,P=0.004)激活程度高于下楼梯时;(3)有跌倒风险的老年人上楼梯股外侧肌(Z=-2.613,P=0.009)、腓肠肌内侧(Z=-2.286,P=0.022)和下楼梯股外侧肌(Z=-2.368,P=0.018)激活程度小于没有跌倒风险的老年人;(4)基于肌电信号建立的老年人楼梯跌倒预测模型预测能力、拟合度和区分度良好,模型系数的Omnibus检验的P值为0.010,Hosmer-Lemeshow检验P值为0.214,曲线下面积上楼梯股外侧肌RMS=0.856,P=0.009;(5)模型以上楼梯股外侧肌RMS值38.64为分界值,老年人上楼梯股外侧肌RMS每减小一个单位,楼梯跌倒风险增加0.952倍。